The present invention relates to a system for interconnecting a plurality of controlled devices in such a manner that the controller can address any one of the controlled devices. More particularly, this invention relates to a device connection system wherein a unit address depends only upon the position in which that unit is located in a chain of devices which are connected to a controller.
In a bus tap type of device interconnection system, a plurality of controlled devices are often connected to a signal bus that is controlled by a single set of control electronics. For example, several cassette drives may be connected to a computer via a single bus and controller. In such systems each unit is assigned an address. When the controller transmits an address, the proper unit responds. The unit address to be assigned to a particular controlled device is usually selected by a thumbwheel switch on the unit. This method is expensive and is subject to human error. For example, the thumbwheel can be erroneously set to the wrong number, or a correctly set thumbwheel switch can be bumped, thereby resulting in an incorrect setting.
In a master-slave type interconnection system, the master controlled device is connected to the controller, and, like the previously described bus tap system, only a single interface board is required at the controller. The remainder of the controlled devices, the slave devices, are connected to the master controlled device. Device code selection and control is performed in the master controlled device. This system is disadvantageous in that the master device is different from the slave devices, and the cost and complexity of the system is therefore increased.
In a multi interface device connection system each device is separately connected by an electronic card to the signal bus of the controller. This system is disadvantageous in that each device requires an electronic board connected to the signal bus, and device codes must be manually selected on those boards.